1. Field of the Invention
This invention relates to a method for producing an electrically conductive compound yarn from an electrically conductive metallic portion and a textile portion. This invention also relates to the electrically conductive yarn itself produced in accordance with the method, and to its use.
2. Description of Prior Art
Some attempts for producing electrically conductive textile materials have been attempted. Woven goods with metal threads inserted are known. So that the weaving of metal threads causes fewer problems at the loom, it was attempted to process the metal threads into a mixed yarn or a compound yarn.
For example, a production method for such a compound yarn is known from PCT International Application WO 93/24689. This is a compound yarn made of textile fibers of the same or different types, which are twisted with a metal wire of annealed, silvered or gilded copper or of annealed stainless steel, with a diameter between 0.008 and 0.05 mm. After twisting the compound yarn, the metal wire essentially is located in an axial longitudinal direction between mutual contact zones of the individual textile fibers.
In this case the metal wire remains somewhat stretched inside the compound yarn. The bond between the partial yarn and the wire is not always sufficient and there is a danger that the compound yarn becomes separated again in the course of further processing.
Another comparable method is described in European Patent Reference EP-A-0 644 283. Here, metallic wires and textile threads when brought together are twisted with each other. An advantage of this compound yarn is that the bond between the textile threads and the metal wires is very good. However, there is a disadvantage that the metal wires are already considerably mechanically prestressed and the compound yarn is relatively stiff and prone to break.
The use of a metal-containing compound yarn for screening is known from European Patent Reference EP-A-0 250 260, wherein the compound yarn has a core and a sheath. The compound yarn comprises metallic and non-metallic fibers, wherein the core essentially contains a continuous metallic filament, reinforced by a non-metallic filament or yarn, and the sheath contains a non-metallic filament or yarns, which are wound around the core and constitute at least 70% of the surface of the compound yarn, wherein the non-metallic fibers are made of chemical or synthetic fibers. Here, too, the compound yarn is created by twisting and has the associated advantages and disadvantages.
A method for the production of a compound yarn, which actually could be identified as a mixed yarn, is taught by U.S. Pat. No. 3,987,613, which in contrast to previously described compound yarns is not created by twisting. Short copper fibers of a diameter of 0.025 mm and a length of approximately 40 mm are mixed with textile fibers prior to producing the yarn and are subsequently spun into a yarn together. The spun mixed yarn contains between 0.25 and 15 weight-percent of metallic fibers. So that such a spun mixed yarn could become electrically conductive, the mixed yarn should contain a considerably higher percentage of metal fibers which have sufficient contact with each other in the yarn itself. These metal fibers are naturally distributed over the entire yarn cross section. Since they are also present at the yarn surface, they cause considerable wear of the respective processing devices and machines during spinning and during any further processing, which is problematic.